Introduction to the Principles and Components of Distributed Fiber Optic Temperature Measurement Systems (DTS)

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Distributed Fiber Optic Raman Temperature Measurement DTS system 

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is based on the optical time domain reflection (OTDR)

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 principle of optical fibers and the Raman scattering effect of optical fibers

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The laser pulse interacts with the fiber molecules 

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and a variety of scattering occurs

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such as Rayleigh scattering

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Brillouin scattering and Raman scattering

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Raman scattering is due to the thermal vibration of the fiber optic molecules

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which produces a light-Stokes light that is longer than the wavelength of the light source

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 and a Anti-Stokes light that is shorter than the wavelength of the light source

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The fiber is modulated by the external temperature

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causing the Anti-Stokes light intensity in the fiber to change

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Anti-Stokes to Stokes ratio provides an absolute indication of temperature

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the use of this principle to achieve the distributed measurement of the temperature field along the optical fiber

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combined with high-quality pulsed light source and high-speed signal acquisition and processing technology

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we can get the accurate temperature value of all points along the fiber

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According to the above principle

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 we look at the specific realization of the system

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First of all, the DTS system needs a pulsed laser

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 the output light is 1550nm

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the typical pulse width is 10ns

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peak power: 10~30W

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the trigger mode is: external trigger

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and the pigtail type is a multimode fiber of 62.5/125

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The output port of the pulsed laser

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is connected to the 1550 port of the 1x3 Raman WDM module

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then the temperature measurement fiber optic cable is connected to the COM port of the WDM

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and the remaining 1450 and 1660 ports are connected to the two input ports of the dual-channel APD respectively

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The dual-channel APD photoelectric converter 

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converts the anti-Stokes and Stokes light into electrical signals

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the electrical signals are output through the SMA interface 

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and connected to the two acquisition channels of the acquisition card with RF cables

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The capture card has an integrated signal trigger function

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Connect the trigger interface to the laser's SMA trigger input via the RF cable

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This completes all wiring

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The acquisition card has a built-in averaging algorithm

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 The data collected by the two channels of the acquisition card 

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can be plotted as two real-time curves

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The ratio of the two curves

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 has an approximately linear relationship with the temperature

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 By calibrating the temperature of the test fiber optic cable

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we can obtain the relationship between the temperature and the ratio

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realize the function of temperature measurement of fiber optic cables

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Of course

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the reality also needs to take into account the length of the fiber optic cable、

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optical power、attenuation and other factors, and do the corresponding compensation algorithm

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To realize the high precision DTS temperature measurement system

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it still needs technology

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 We have made all the equipment for the DTS system mentioned above into a hardware development kit

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 so please inquire if you are interested.